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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Nov 2023, 2:45 pm   #1
ScottBouch
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Default Circuit simulation request favour - multivibrator flasher circuit

Hi all,

Would someone mind simulating a circuit for me please? I ask as It'd take me too long to install/learn the software for this one task.

In the bottom right corner of this diagram is a "Flasher and Excitation Unit" made by Page Engineering.

https://www.scottbouch.com/mcfs/ligh...y-standard.jpg

This video shows the red lamps flashing due to this multivibrator flasher circuit, including all component typers and values. I don't know though if any modern electronics simulator software would include GET110 and GET111 transistors though? Maybe a generic model could be used?

https://scottbouch.com/English-Elect...on-getters.mp4

Transistor specs found online (can't find a real datasheet):
GET110: https://alltransistors.com/transisto...ansistor=35567
GET111: https://alltransistors.com/transisto...ansistor=35568

I'm not 100% sure that the frequency recorded in the video is correct, as the capacitors in this unit will be as old as the hills. I'm interested to find out what the design frequency was for the flashing lamps to verify the video frequency.

This is for an EE Lightning flight simulator I'm designing, the flashing will be carried out by the simulator software model, a model which I intend to make as accurate as possible, including details like the flashing frequency.

Flasher and Excitation unit terminal & function:

R = output to 2x 3.5W lamps in parallel (sourcing current from unit, lamps to earth)
V = output to 1x 40mA lamp (sourcing current from unit, lamp to earth)
Z = 24 V to 28 V power supply (via lower high-speed relay contact)
f & U = earth / 0 V

Many thanks, Scott
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Old 17th Nov 2023, 2:58 pm   #2
Keith956
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

Scott, the diagram does not seem to heve the capacitor values. It only gives the base resistors, as 10K.

You can calculate the frequency as F = 1 / (1.4 * C * R) but you need to know both C and R values.
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Old 17th Nov 2023, 3:30 pm   #3
ScottBouch
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

Oh of course! What an idiot - I didn't notice that. Well spotted Keith.

Well.. in absence of the manual for the unit, and not having access to a unit to look inside, this project may have to wait until I can do further research.

Cheers, Scott
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Old 17th Nov 2023, 4:18 pm   #4
cmjones01
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

That circuit looks like a standard "flip-flop" astable multivibrator, very popular as a beginner's electronics project before the 555 took over everything. The GET110 transistors are just there to drive a larger current into the relay coils, as far as I can see. Its flash frequency won't depend much on the characteristics of the transistors, so it can be analysed using generic devices. There's a standard formula for the approximate flash frequency, which Keith has quoted above.

Chris
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Old 17th Nov 2023, 4:25 pm   #5
Ed_Dinning
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

Hi Scott, cheat a little and us a modern 555 timer

Ed
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Old 17th Nov 2023, 4:30 pm   #6
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

With the typical tolerance on period electrolytic capacitors, the flashing rate would have had quite a large spread.

That simple multivibrator circuit has a well known bug. They can turn on in a stalled condition with both lights lit. It's probably as well that you're doing it in software. The stall condition depends on the balance of the circuit and the rate the supply voltage comes up. There is a way to prevent it at the cost of a couple of diodes.

David
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Old 17th Nov 2023, 4:32 pm   #7
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

The 555 itself isn't bug free, Ed. They have a habit of going unstable on output transitions, adding a burst of fast pulses. Sometimes you just can't win.

David
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Old 17th Nov 2023, 8:48 pm   #8
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

Quote:
Originally Posted by Radio Wrangler View Post
With the typical tolerance on period electrolytic capacitors, the flashing rate would have had quite a large spread.

That simple multivibrator circuit has a well known bug. They can turn on in a stalled condition with both lights lit. It's probably as well that you're doing it in software. The stall condition depends on the balance of the circuit and the rate the supply voltage comes up. There is a way to prevent it at the cost of a couple of diodes.

David
Yes, in my other recent project fixing the warnin alarm unit (based on x2 multivibrators) saw that starter circuit, as without it there is a chance of it locking up.
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Old 17th Nov 2023, 8:54 pm   #9
ScottBouch
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Default Re: Circuit simulation request favour - multivibrator flasher circuit

Quote:
Originally Posted by cmjones01 View Post
That circuit looks like a standard "flip-flop" astable multivibrator, very popular as a beginner's electronics project before the 555 took over everything. The GET110 transistors are just there to drive a larger current into the relay coils, as far as I can see. Its flash frequency won't depend much on the characteristics of the transistors, so it can be analysed using generic devices. There's a standard formula for the approximate flash frequency, which Keith has quoted above.

Chris
One thing I might do is try the formula with some standard capacitor values, bearing in mind they may have been metallised film, or germanium, or possibly electrolytic (early 1960's design), a list of NPV standard capacitor sizes would be a start. Then step throuh values to find a frequency near to the frequency in the video.

Cheers, Scott
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